Remington REM-05-240-GH Service Manual download pdf (Page 21)

Suction

Line

Evaporator

Coil

Metering

Device

Refrigerant

Strainer

Discharge

Line

Condenser

Coil

Compressor

Refrigerant Drier

Liquid

Line

A good understanding of the basic operation of the

refrigeration system is essential for the service technician.

Without this understanding, accurate troubleshooting of

refrigeration system problems will be more difcult and time

consuming, if not (in some cases) entirely impossible. The

refrigeration system uses four basic principles (laws) in its

operation they are as follows:

1. “Heat always ows from a warmer body to a cooler

body.”

2. “Heat must be added to or removed from a substance

before a change in state can occur”

3. “Flow is always from a higher pressure area to a lower

pressure area.”

4. “The temperature at which a liquid or gas changes state

is dependent upon the pressure.”

The refrigeration cycle begins at the compressor. Starting

the compressor creates a low pressure in the suction line

which draws refrigerant gas (vapor) into the compressor.

The compressor then “compresses” this refrigerant, raising

its pressure and its (heat intensity) temperature.

The refrigerant leaves the compressor through the discharge

Line as a hot High pressure gas (vapor). The refrigerant

enters the condenser coil where it gives up some of its

heat. The condenser fan moving air across the coil’s nned

surface facilitates the transfer of heat from the refrigerant to

the relatively cooler outdoor air.

When a sufcient quantity of heat has been removed from

the refrigerant gas (vapor), the refrigerant will “condense”

(i.e. change to a liquid). Once the refrigerant has been

condensed (changed) to a liquid it is cooled even further by

the air that continues to ow across the condenser coil.

The PTAC design determines at exactly what point (in

the condenser) the change of state (i.e. gas to a liquid)

takes place. In all cases, however, the refrigerant must be

totally condensed (changed) to a Liquid before leaving the

condenser coil.

The refrigerant leaves the condenser Coil through the liquid

line as a warm high pressure liquid. It next will pass through

the refrigerant drier (if so equipped). It is the function of the

drier to trap any moisture present in the system, contaminants,

and large particulate matter.

The liquid refrigerant next enters the metering device. The

metering device is a capillary tube. The purpose of the

metering device is to “meter” (i.e. control or measure) the

quantity of refrigerant entering the evaporator coil.

In the case of the capillary tube this is accomplished (by

design) through size (and length) of device, and the pressure

difference present across the device.

Since the evaporator coil is under a lower pressure (due to

the suction created by the compressor) than the liquid line,

the liquid refrigerant leaves the metering device entering the

evaporator coil. As it enters the evaporator coil, the larger

area and lower pressure allows the refrigerant to expand

and lower its temperature (heat intensity). This expansion is

often referred to as “boiling”. Since the unit’s blower is moving

indoor air across the nned surface of the evaporator coil,

the expanding refrigerant absorbs some of that heat. This

results in a lowering of the indoor air temperature, hence the

“cooling” effect.

The expansion and absorbing of heat cause the liquid

refrigerant to evaporate (i.e. change to a gas). Once the

refrigerant has been evaporated (changed to a gas), it is

heated even further by the air that continues to ow across

the evaporator coil.

The particular system design determines at exactly what

point (in the evaporator) the change of state (i.e. liquid to a

gas) takes place. In all cases, however, the refrigerant must

be totally evaporated (changed) to a gas before leaving the

evaporator coil.

The low pressure (suction) created by the compressor

causes the refrigerant to leave the evaporator through the

suction line as a cool low pressure vapor. The refrigerant then

returns to the compressor, where the cycle is repeated.

REFRIGERATION SEQUENCE OF OPERATION

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Remington REM-05-240-GH Service Manual Page 21

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